1,832 research outputs found
Modeling cosmic ray anisotropies near 10(18) eV
A galactic magnetic field reversal near the Sagittarius spiral arm may be responsible for the southern excess (or northern shortage) of cosmic rays near 10 to the 18th power eV. The north-south asymmetry produced by such a reversal would increase with energy in the same manner as the observed asymmetry. The existence of a reversal has been inferred from analyses of Faraday rotation measures
Statistics of conductance and shot-noise power for chaotic cavities
We report on an analytical study of the statistics of conductance, , and
shot-noise power, , for a chaotic cavity with arbitrary numbers of
channels in two leads and symmetry parameter . With the theory
of Selberg's integral the first four cumulants of and first two cumulants
of are calculated explicitly. We give analytical expressions for the
conductance and shot-noise distributions and determine their exact asymptotics
near the edges up to linear order in distances from the edges. For a
power law for the conductance distribution is exact. All results are also
consistent with numerical simulations.Comment: 7 pages, 3 figures. Proc. of the 3rd Workshop on Quantum Chaos and
Localisation Phenomena, Warsaw, Poland, May 25-27, 200
Induced Ginibre ensemble of random matrices and quantum operations
A generalisation of the Ginibre ensemble of non-Hermitian random square
matrices is introduced. The corresponding probability measure is induced by the
ensemble of rectangular Gaussian matrices via a quadratisation procedure. We
derive the joint probability density of eigenvalues for such induced Ginibre
ensemble and study various spectral correlation functions for complex and real
matrices, and analyse universal behaviour in the limit of large dimensions. In
this limit the eigenvalues of the induced Ginibre ensemble cover uniformly a
ring in the complex plane. The real induced Ginibre ensemble is shown to be
useful to describe statistical properties of evolution operators associated
with random quantum operations, for which the dimensions of the input state and
the output state do differ.Comment: 2nd version, 34 pages, 5 figure
In Search of a Source for the 320 Eev Fly's Eye Cosmic Ray
The 320 EeV air shower detected by the Fly's Eye poses an important problem.
Careful analysis of pathlength limitations for the possible particle types due
to cosmic background radiation verifies that the particle very likely traveled
less than 50 Mpc from its source. The best candidates for accelerating
particles to such high energies are the very powerful radiogalaxies, however
they are all more than 100 Mpc distant. Our search finds no likely source
within 50 Mpc in the direction from which the particle arrived. This prompts
consideration of less likely astrophysical sources, like M82, as well as
non-standard mechanisms like cosmic string annihilation. It is also conceivable
that the air shower was produced by some non-standard particle whose pathlength
is unlimited because it does not interact with the cosmic background radiation.
A less radical alternative is that relatively strong magnetic fields deflected
the particle's path through a large angle, so it could have originated at a
nearby radiogalaxy at an earlier time of strong activity.Comment: 27 pages, LaTeX, figures available by anonymous ftp, to appear in ApJ
(3/1/95
Role of electron-electron and electron-phonon interaction effect in the optical conductivity of VO2
We have investigated the charge dynamics of VO2 by optical reflectivity
measurements. Optical conductivity clearly shows a metal-insulator transition.
In the metallic phase, a broad Drude-like structure is observed. On the other
hand, in the insulating phase, a broad peak structure around 1.3 eV is
observed. It is found that this broad structure observed in the insulating
phase shows a temperature dependence. We attribute this to the electron-phonon
interaction as in the photoemission spectra.Comment: 6 pages, 8 figures, accepted for publication in Phys. Rev.
Random Bistochastic Matrices
Ensembles of random stochastic and bistochastic matrices are investigated.
While all columns of a random stochastic matrix can be chosen independently,
the rows and columns of a bistochastic matrix have to be correlated. We
evaluate the probability measure induced into the Birkhoff polytope of
bistochastic matrices by applying the Sinkhorn algorithm to a given ensemble of
random stochastic matrices. For matrices of order N=2 we derive explicit
formulae for the probability distributions induced by random stochastic
matrices with columns distributed according to the Dirichlet distribution. For
arbitrary we construct an initial ensemble of stochastic matrices which
allows one to generate random bistochastic matrices according to a distribution
locally flat at the center of the Birkhoff polytope. The value of the
probability density at this point enables us to obtain an estimation of the
volume of the Birkhoff polytope, consistent with recent asymptotic results.Comment: 22 pages, 4 figure
Statistics of quantum transport in chaotic cavities with broken time-reversal symmetry
The statistical properties of quantum transport through a chaotic cavity are
encoded in the traces \T={\rm Tr}(tt^\dag)^n, where is the transmission
matrix. Within the Random Matrix Theory approach, these traces are random
variables whose probability distribution depends on the symmetries of the
system. For the case of broken time-reversal symmetry, we present explicit
closed expressions for the average value and for the variance of \T for all
. In particular, this provides the charge cumulants \Q of all orders. We
also compute the moments of the conductance . All the
results obtained are exact, {\it i.e.} they are valid for arbitrary numbers of
open channels.Comment: 5 pages, 4 figures. v2-minor change
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